silent as the grave

Perhaps connected to the idea of taking a secret to the grave, or the idea that dead men tell no tales.

• "The investigation is ongoing, but all the suspects have been silent as the grave so far."
• "“Livesey,” returned the squire, “you are always in the right of it. I’ll be as silent as the grave.”"
• "“Well, then, if you’re bound to go, I’ll tell you the way to do when you get to the village. Shut the door and blindfold the doctor tight and fast, and make him swear to be silent as the grave, and put a purse full of gold in his hand, […]"
• "The abandoned village is silent as the grave."

• silent as the tomb